Poling method, poling device for piezoelectric element and inkjet print head

ABSTRACT

There is provided a poling method for a piezoelectric element, including performing preliminary poling of the piezoelectric element twice or more with different voltages and measuring conductance of the piezoelectric element with regard to respective voltage, establishing a relational expression between the voltage and the conductance of the piezoelectric element, calculating targeted conductance required to exhibit a targeted piezoelectric characteristic of the piezoelectric element, and selecting a targeted voltage level corresponding to the targeted conductance and performing final poling of the piezoelectric element at the targeted voltage level.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority of Korean Patent Application No.10-2013-0015793 filed on Feb. 14, 2013, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a piezoelectric element, and moreparticularly, to a poling method and a poling device for a piezoelectricelement capable of improving poling reliability of a piezoelectricelement and shortening a required poling time, as well as to an inkjetprint head.

2. Description of the Related Art

A piezoelectric element has been widely used as a driving unit forinkjet print heads, micro pumps, micro fluid discharge devices andvarious other small devices. Piezoelectric elements generate apredetermined degree of physical displacement through current suppliedthereto through an electrode, to provide required driving force torespective device.

Generally, displacement of the piezoelectric element varies according toa poling condition thereof. For example, the displacement of apiezoelectric element may vary according to a magnitude of polingvoltage and/or the time of the application of poling voltage, or thelike. Therefore, the displacement of the piezoelectric element may bearbitrarily adjusted by adjusting the poling conditions according to thetype of device using the piezoelectric element.

However, even though the displacement of the piezoelectric element maybe performed under the same poling conditions, the displacement of thepiezoelectric element may vary according to piezoelectriccharacteristics of the piezoelectric element, the manufacturingenvironment of the piezoelectric element, and the manufacturer of thepiezoelectric element. Thus, a plurality of piezoelectric elements poledunder the same conditions may have different degrees of displacement,thereby reducing the reliability of devices that use a plurality ofpiezoelectric elements as actuators (for example, an inkjet print head).

As related art aimed at solving the above-described problem, there isprovided the following related art document, disclosing technology formeasuring displacement of a piezoelectric element measured in aplurality of poling processes to calculate a final poling voltage.

However, the displacement of the piezoelectric element is changed foreach portion of the piezoelectric element and the correlation betweenthe obtained displacement and the poling voltage does not necessarilyhave a proportional relationship, such that it may be difficult toobtain a reliable final poling voltage.

Further, it takes a significant amount of time to obtain the finalpoling voltage disclosed in the following related art document, suchthat it may be difficult to pole the plurality of piezoelectric elementssimultaneously.

RELATED ART DOCUMENT

KR 2009-0005631A

SUMMARY OF THE INVENTION

An aspect of the present invention provides a poling method and a polingdevice for a piezoelectric element, capable of improving polingreliability of a piezoelectric element and shortening a required polingtime, as well as an inkjet print head.

According to an aspect of the present invention, there is provided apoling method for a piezoelectric element, including: performingpreliminary poling of the piezoelectric element twice or more withdifferent voltages and measuring conductance of the piezoelectricelement with regard to respective voltage; establishing a relationalexpression between the voltage and the conductance of the piezoelectricelement; calculating targeted conductance required to exhibit a targetedpiezoelectric characteristic of the piezoelectric element; and selectinga targeted voltage level corresponding to the targeted conductance andperforming final poling of the piezoelectric element at the targetedvoltage level.

The performing of the preliminary poling may include: performing firstpreliminary poling of the piezoelectric element at a first voltage leveland measuring a first conductance of the piezoelectric element for thefirst voltage level; and performing second preliminary poling of thepiezoelectric element at a second voltage level and measuring a secondconductance of the piezoelectric element for the second voltage level.

The second voltage level may be higher than the first voltage level.

The voltage performing the preliminary poling may be set to be lowerthan the targeted voltage level.

The piezoelectric element may be a plurality of actuators mounted in aninkjet print head.

The targeted piezoelectric characteristic may indicate a discharge speedof ink.

According to an aspect of the present invention, there is provided apoling device for a piezoelectric element, including: a plurality ofvoltage generation units generating different magnitudes of voltage forpoling a plurality of piezoelectric elements; a plurality of conductancemeasurement units measuring conductance of the piezoelectric element;and a control unit storing voltage generated by the voltage generationunit and conductance measured by the conductance measurement unit,respectively, and setting target voltages for performing final poling ofthe plurality of piezoelectric elements, based on a relationalexpression between the stored voltage and the conductance of thepiezoelectric element, respectively.

The control unit may individually set final poling voltages for theplurality of piezoelectric elements.

The control unit may set the final poling voltages for the plurality ofpiezoelectric elements simultaneously.

According to an aspect of the present invention, there is provided aninkjet print head, including: a plurality of piezoelectric elements forproviding driving force to a plurality of pressure chambers, whereinuniformity (% range) of the plurality of piezoelectric elements is 30%or less.

The uniformity (% range) may be represented by a percentage (%) afterdividing a difference between a maximum displacement and a minimumdisplacement of the piezoelectric element by an average displacement.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a cross-sectional perspective view of an inkjet print head;

FIG. 2 is a configuration diagram of a poling device for a piezoelectricelement according to an embodiment of the present invention;

FIG. 3 is a flow chart of a poling method for a piezoelectric elementaccording to an embodiment of the present invention;

FIG. 4 is a diagram illustrating a relationship between conductance andvoltage;

FIG. 5 is a diagram illustrating a relationship between conductance anddisplacement of a piezoelectric element;

FIG. 6 is a diagram illustrating a relationship between conductance andink discharge speed; and

FIG. 7 is a flow chart of a poling method for a piezoelectric elementaccording to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. The invention may,however, be embodied in many different forms and should not be construedas being limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the invention to thoseskilled in the art.

Performance of a device in which a plurality of piezoelectric elementsare provided may depend on piezoelectric characteristics of thepiezoelectric elements. For example, quality of discharged inkdischarged from an inkjet print head may depend on the piezoelectriccharacteristics of the piezoelectric element. In particular, thepiezoelectric element may have different piezoelectric characteristicsaccording to a manufacturing environment thereof, such that it may bedifficult to realize uniform discharge characteristics in all nozzlesprovided in the inkjet print head.

Embodiments of the present invention may be provided to solve thisproblem, and may perform the poling of the piezoelectric element in thestate in which the piezoelectric element is mounted in the inkjet printhead to realize uniform discharge characteristics in the inkjet printhead.

Further, according to the embodiment of the present invention, thepoling of the piezoelectric element using electrical characteristics(impedance or conductance) of the piezoelectric element may beperformed, thereby rapidly performing poling of the piezoelectricelement.

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings.

In describing the present invention below, terms indicating componentsof the present invention will be named in consideration of functionsthereof. Therefore, the terms should not be understood as limiting thetechnical components of the present invention.

FIG. 1 is a cross-sectional perspective view of an inkjet print head,FIG. 2 is a configuration diagram of a poling device for a piezoelectricelement according to an embodiment of the present invention, FIG. 3 is aflow chart of a poling method for a piezoelectric element according toan embodiment of the present invention, FIG. 4 is a diagram illustratinga relationship between conductance and voltage, FIG. 5 is a diagramillustrating a relationship between conductance and displacement of apiezoelectric element, FIG. 6 is a diagram illustrating a relationshipbetween conductance and ink discharge speed, and FIG. 7 is a flow chartof a poling method for a piezoelectric element according to anotherembodiment of the present invention.

A structure of the inkjet print head in which a plurality ofpiezoelectric elements are mounted will be briefly described withreference to FIG. 1. For reference, it is to be noted that “actuator” isused herein as a term having the same meaning as “piezoelectric element”and these components may be denoted by the same reference numeral 140.

An inkjet print head 100 may include a manifold 110, a pressure chamber120, a nozzle 130, and an actuator 140. Herein, the manifold 110 maysupply ink to a plurality of pressure chambers 120 and the pressurechamber 120 may store an amount of ink required for a single discharge.In addition, the actuator 140 may provide driving force required todischarge the ink in the pressure chamber 120 through the nozzle 130.

The plurality of pressure chambers 120 may have the same size so as todischarge the same amount of ink. Similarly, each actuator 140 includesa piezoelectric element having the same piezoelectric characteristics soas to provide the same magnitude of driving force to the pressurechamber 120.

However, as described above, the piezoelectric element configuring theactuator 140 may have different piezoelectric characteristics inresponse to the manufacturing environment thereof. For this reason, evenin the case that the actuator 140 is driven by the same electricalsignal, the amount of ink discharged through a respective nozzle 130 maybe different.

In the embodiment of the invention to solve the problem, the poling ofthe piezoelectric element may be performed in the state in which thepiezoelectric element is mounted in the inkjet print head 100. In thiscase, poling conditions (that is, poling voltage) of the piezoelectricelement may be adjusted by being compared with discharge characteristics(for example, an amount of discharged ink or an ink discharge speed) ofthe nozzle 130.

However, the discharge characteristics of the nozzle cannot actually bemeasured, and therefore a final poling voltage of the piezoelectricelement may be determined by measuring other characteristics of thepiezoelectric element. For example, the final poling voltage of thepiezoelectric element may be adjusted by measuring the displacement ofthe piezoelectric element.

However, the displacement of the piezoelectric element 140 in the inkjetprint head 100 is nonlinearly changed in response to a length directionof the piezoelectric element 140, such that determination of the finalpoling voltage based on the displacement of the piezoelectric element140 may deteriorate reduces reliability. Therefore, when thedisplacement of the piezoelectric element 140 is used to determine thefinal poling voltage of the piezoelectric element 140, the displacementof the piezoelectric element 140 needs to be measured at multiplepoints. However, the method requires considerable time, unsuitable for adevice such as the inkjet print head in which the plurality ofpiezoelectric elements 140 are mounted.

Therefore, a poling method and a poling device according to anembodiment of the present invention are provided.

The poling method for a piezoelectric element according to theembodiment of the present invention may use the electricalcharacteristics (for example, impedance or conductance) of thepiezoelectric element to determine the final poling voltage of thepiezoelectric element. Herein, the impedance and conductance in theelectrical characteristics of the piezoelectric element may easily bemeasured. Further, the impedance and conductance of the piezoelectricelement has a generally linear relationship with the dischargecharacteristics of the nozzle, which may be relatively very effective inimproving the discharge characteristics of the inkjet print head.

Herein, a poling device 200 for a piezoelectric element according to anembodiment of the present invention may include a voltage generationunit 210, a conductance measurement unit 220, and a control unit 230 asillustrated in FIG. 2.

The voltage generation unit 210 is electrically connected to the inkjetprint head 100 and may apply a predetermined voltage to the plurality ofactuators 140 or piezoelectric elements. In addition, the voltagegeneration unit 210 may apply the same level of voltage to the pluralityof actuators 140 simultaneously, or selectively apply a different levelof voltage to respective actuators 140. Herein, the magnitude of voltageapplied by the voltage generation unit 210 may be adjusted by thecontrol unit 230.

The conductance measurement unit 220 is electrically connected to theinkjet print head 100 and may measure the conductance of the actuator140 or the piezoelectric element. The conductance measurement unit 220may send the measured conductance of the actuator 140 or the measuredconductance of the piezoelectric element to the control unit 230. Forreference, the embodiment of the present invention is described asincluding the conductance measurement unit 220 to measure theconductance of the actuator 140 or the piezoelectric element, but animpedance measurement unit for measuring the impedance of the actuator140 or the piezoelectric element may be used instead of the conductancemeasurement unit 220.

The control unit 230 may be connected to the voltage generation unit 210and the conductance measurement unit 220. In addition, the control unit230 may adjust the level of voltage generated by the voltage generationunit 210 and may store the conductance of the actuator 140 or thepiezoelectric element that is sent from the conductance measurement unit220. In addition, the control unit 230 may establish a relationalexpression between a magnitude of voltage applied to the piezoelectricelement and measured conductance. To this end, the control unit 230 mayinclude a separate operation unit. In addition, the control unit 230 mayset the final poling voltage (targeted voltage level described inclaims) of the piezoelectric element based on the established relationalexpression. Herein, the targeted voltage level may be obtained bysubstituting a conductance value corresponding to a targetedpiezoelectric characteristic into the relational expression.

Next, a poling method for a piezoelectric element according to anembodiment of the present invention will be described with reference toFIG. 3.

The poling method for a piezoelectric element according to theembodiment of the present invention may include a primary preliminarypoling process, a primary conductance measurement process, a secondarypreliminary poling process, a secondary conductance measuring process, atargeted conductance selecting process, and a final poling process.

1) Primary Preliminary Poling Process (S110)

In the present process, a primary voltage may be applied to theplurality of piezoelectric elements 140 mounted in the inkjet print head100. Herein, the primary voltage may be a voltage significantly lowerthan the final poling voltage of the piezoelectric element that is knownin the art.

Meanwhile, in the present process, the primary voltage may be applied tothe plurality of piezoelectric elements 140 simultaneously. However, theprimary voltage is not necessarily applied to all of the piezoelectricelements 140. For example, the primary voltage may only be applied to apart of the plurality of piezoelectric elements 140, as a sample. Forreference, a frequency of the primary voltage may be 1 kHz .

2) Primary Conductance Measuring Process (S120)

In the present process, the primary conductance of the piezoelectricelement 140 may be measured in the state in which the primary voltage isapplied. Herein, the primary conductance may be individually measuredfor respective piezoelectric elements 140. The measured primaryconductance may be transmitted to the control unit 230. Meanwhile, theprimary conductance transmitted to the control unit 230 may be storedalong with the primary voltage.

3) Secondary Preliminary Poling Process (S130)

In the present process, a secondary voltage may be applied to theplurality of piezoelectric elements 140 mounted in the inkjet print head100. Herein, the secondary voltage may be a voltage higher than theprimary voltage. Further, the secondary voltage may have a numericalvalue approaching the final poling voltage of the piezoelectric elementthat is known in the art. In this case, the reliability for the finalpoling voltage obtained by using the relational expression betweenvoltage and conductance may be improved.

In the present process, similar to the primary voltage, the secondaryvoltage may be applied to the plurality of piezoelectric elements 140simultaneously. However, the secondary voltage is not necessarilyapplied to all the piezoelectric elements 140 and the secondary voltagemay only be applied to apart of the plurality of piezoelectric elements140, as a sample . For reference, a frequency of the secondary voltagemay be 1 kHz.

4) Secondary Conductance Measuring Process (S140)

In the present process, the secondary inductance of the piezoelectricelement 140 may be measured in the state in which the secondary voltageis applied. Herein, the secondary conductance may be individuallymeasured for respective piezoelectric elements 140, similar to theprimary conductance. Further, the measured secondary conductance may betransmitted to the control unit 230. The secondary conductance sent tothe control unit 230 may be stored along with the secondary voltage .For reference, the measurement frequency of the secondary conductancemay be 1 kHz.

5) Targeted Conductance Selecting Process (S150)

In the present process, the relational expression between voltage andconductance is established and the targeted conductance may be selectedbased on the established relational expression. Herein, the relationalexpression between voltage and conductance may be established bycalculating linearity between voltage, and conductance and separaterelational expressions for respective piezoelectric elements may beestablished.

The targeted conductance may be applied to the selection of theconductance value corresponding to the targeted piezoelectriccharacteristic of the piezoelectric element. Herein, the selection ofthe targeted conductance may be performed using the relationship betweenpiezoelectric characteristics and conductance obtained by an experiment(for example, see FIGS. 5 and 6). 6) Final Poling Process (S160)

In the present process, the final poling voltage (or targeted voltagelevel) of the piezoelectric element is set and the piezoelectric elementmay be poled with the set targeted voltage level. In addition, thepreliminary poling of the piezoelectric element may be performed withthe targeted voltage and the conductance of the piezoelectric elementmay be measured.

Herein, when a deviation between the measured conductance and thetargeted conductance is within a range of error, the final poling of thepiezoelectric element may be performed with the targeted voltage. Unlikethis, when the deviation between the measured conductance and thetargeted conductance deviates from the error range, the targeted voltagelevel may be corrected according to the magnitude of the deviation.

For reference, unlike the preliminary poling, the poling working underthe targeted voltage conditions may be performed under the hightemperature and high pressure state and may be performed for a longertime than the preliminary poling.

Meanwhile, the correlation between the impedance or conductance of thepiezoelectric element and the discharge characteristic of the nozzle canbe appreciated with reference to FIGS. 4 to 6, and the correlation hasbeen confirmed through repetitive experimentation.

That is, the conductance of the piezoelectric element is substantiallyin proportion to the magnitude of the poling voltage as illustrated inFIG. 4. Therefore, the relational expression between the conductance andvoltage of the piezoelectric element that is a poling object maybeestablished and the final poling voltage of the piezoelectric elementmay be reliably established.

In addition, it can be confirmed that the conductance of thepiezoelectric element has a substantially linear relationship with thedisplacement of the piezoelectric element and the discharge speed of inkas illustrated in FIGS. 5 and 6.

Therefore, when the relational expression between the poling voltageapplied to the piezoelectric element and the conductance of thepiezoelectric element is clearly established, the displacementcharacteristic of the piezoelectric element and the dischargecharacteristic of ink may be set as required.

For reference, Table 1 shows the characteristics of the piezoelectricelement poled with the same magnitude of voltage and the dischargecharacteristics of the inkjet print head in which the correspondingpiezoelectric element is mounted.

TABLE 1 Displace- Piezoelectric Volume Speed Conductance Frequency mentElement NO. [

] [m/s] [

] [kHz] [nm] CF0101_01-10 38.2 2.3 460.9 695.6 −52.1 CF0101_01-11 39.52.4 490.1 687.9 −54.8 CF0101_03-01 41.0 2.6 515.6 685.0 −59.1CF0101_03-03 39.2 2.4 466.9 691.8 −53.6 CF0101_03-04 39.4 2.4 482.4690.7 −54.3 CF0101_03-07 42.2 2.7 524.0 691.0 −59.1 CF0101_03-08 41.02.6 518.5 695.9 −56.1 CF0101_03-11 41.3 2.6 513.7 693.1 −55.6CF0101_03-12 41.7 2.6 685.2 −59.1 CF0101_04-02 40.0 2.4 507.7 692.3−56.4 CF0101_04-03 39.3 2.4 503.8 693.8 −53.4 CF0101_04-05 40.2 2.5489.2 689.0 −56.1 CF0101_04-07 41.8 2.6 535.7 693.1 −59.4 CF0101_04-0938.1 2.3 489.2 699.5 −52.6 CF0101_04-11 41.0 2.6 514.4 693.0 −56.7CF0101_04-12 42.0 2.7 529.1 686.6 −61.8 CF0101_05-01 41.5 2.6 523.7685.7 −58.9 CF0101_05-02 39.9 2.5 513.9 692.1 −54.0 CF0101_05-03 39.22.4 499.5 694.9 −52.4 CF0101_05-06 41.3 2.6 525.6 685.9 −59.6CF0101_05-10 41.3 2.6 549.6 698.3 −54.6 CF0101_07-02 41.2 2.5 496.8693.1 −55.3 CF0101_07-03 39.1 2.4 490.9 693.9 −53.8 CF0101_07-04 39.12.4 497.2 691.6 −54.6 CF0101_07-07 41.8 2.6 537.6 691.3 −61.0CF0101_07-08 39.9 2.5 510.1 696.7 −56.6

indicates data missing or illegible when filed

As can be appreciated from Table 1, the conductance of the piezoelectricelement has a considerable correlation with the volume of dischargedink, the discharge speed of ink, and the displacement of thepiezoelectric element. In addition, respective piezoelectric elementsexhibit different piezoelectric characteristics under the same voltageconditions.

Next, a poling method for a piezoelectric element according to anotherembodiment of the present invention will be described with reference toFIG. 7.

The poling method for a piezoelectric element according to the presentembodiment may include a primary preliminary poling process (S210), aprimary conductance measuring process (S220), a secondary preliminarypoling process (S230), a secondary conductance measuring process (S240),a tertiary preliminary poling process (S250), a tertiary conductancemeasuring process (S260), a relational expression establishing process(S270), a targeted conductance selecting process (S280), and a finalpoling process (S290).

That is, the poling method for a piezoelectric element according to thepresent embodiment may be differentiated from the foregoing embodimentsin that the preliminary poling process is performed three or more times.In other words, in the poling method for a piezoelectric elementaccording to the present embodiment, the preliminary poling process maybe performed three or more times so as to derive the accuratecorrelation and relational expression between voltage and conductance.In addition, the relational expression between voltage and conductancemay be established using a least square method.

In the poling method for a piezoelectric element configured as describedabove, the plurality of preliminary poling processes may be performed tothus establish the relational expression between voltage and conductanceso as to more easily determine the poling voltage through theconductance and more improve the reliability of the determined polingvoltage.

Table 2 shows the conductance of the piezoelectric element measured bythe poling method for a piezoelectric element according to anotherembodiment of the present invention. For reference, the frequency of aprimary to tertiary poling voltages may be 1 kHz.

TABLE 2 Secondary Primary Poling Poling Tertiary Poling FinalConductance (50 V Voltage) (70 V Voltage) (90 V Voltage) Poling Average204.74 317.52 407.21 472.75 Minimum 182.27 254.38 309.75 434.15 Maximum230.15 364.58 470.32 520.12 Uniformity 23.39 34.71 39.43 18.19 (% range)

(Table 2 shows that uniformity (% range) is represented by a percentage(%) after dividing a difference between a maximum displacement and aminimum displacement of the piezoelectric elements mounted in the inkjetprint head by an average displacement)

As can be appreciated from Table 2, in the poling method for apiezoelectric element according to the present embodiment, a finalpoling voltage may be set to more approximate a value of uniformity withregard to the final poling showing in Table 2 above to improve theuniformity of ink ejection from the inkjet print head.

That is, according to the poling method for a piezoelectric elementaccording to the present embodiment, the piezoelectric characteristicsof the piezoelectric elements mounted in the inkjet print head maysubstantially match each other to improve the discharge quality of theinkjet print head.

As set forth above, according to the embodiments of the presentinvention, the poling speed of the piezoelectric element may beimproved.

Further, according to the embodiment of the present invention, thepiezoelectric element having the uniform piezoelectric characteristicsmay be manufactured. Therefore, according to the embodiment of thepresent invention, the operational reliability of devices (for example,an inkjet print head) in which the plurality of piezoelectric elementsare mounted may be improved.

While the present invention has been shown and described in connectionwith the embodiments, it will be apparent to those skilled in the artthat modifications and variations can be made without departing from thespirit and scope of the invention as defined by the appended claims.

What is claimed is:
 1. A poling method for a piezoelectric element,comprising: performing preliminary poling of the piezoelectric elementtwice or more with different voltages and measuring conductance of thepiezoelectric element with regard to respective voltage; establishing arelational expression between the voltage and the conductance of thepiezoelectric element; calculating targeted conductance required toexhibit a targeted piezoelectric characteristic of the piezoelectricelement; and selecting a targeted voltage level corresponding to thetargeted conductance and performing final poling of the piezoelectricelement at the targeted voltage level.
 2. The poling method of claim 1,wherein the performing of the preliminary poling includes: performingfirst preliminary poling of the piezoelectric element at a first voltagelevel and measuring a first conductance of the piezoelectric element forthe first voltage level; and performing second preliminary poling of thepiezoelectric element at a second voltage level and measuring a secondconductance of the piezoelectric element for the second voltage level.3. The poling method of claim 2, wherein the second voltage level ishigher than the first voltage level.
 4. The poling method of claim 1,wherein the voltage performing the preliminary poling is set to be lowerthan the targeted voltage level.
 5. The poling method of claim 1,wherein the piezoelectric element is a plurality of actuators mounted inan inkjet print head.
 6. The poling method of claim 5, wherein thetargeted piezoelectric characteristic indicates a discharge speed ofink.
 7. A poling device for a piezoelectric element, comprising: aplurality of voltage generation units generating different magnitudes ofvoltage for poling a plurality of piezoelectric elements; a plurality ofconductance measurement units measuring conductance of the piezoelectricelement; and a control unit storing voltage generated by the voltagegeneration unit and conductance measured by the conductance measurementunit, respectively, and setting target voltages for performing finalpoling of the plurality of piezoelectric elements, based on a relationalexpression between the stored voltage and the conductance of thepiezoelectric element, respectively.
 8. The poling device of claim 7,wherein the control unit individually sets final poling voltages for theplurality of piezoelectric elements.
 9. The poling device of claim 7,wherein the control unit sets the final poling voltages for theplurality of piezoelectric elements simultaneously.
 10. An inkjet printhead, comprising a plurality of piezoelectric elements for providingdriving force to a plurality of pressure chambers, wherein uniformity (%range) of the plurality of piezoelectric elements is 30% or less, theuniformity (% range) being represented by a percentage (%) afterdividing a difference between a maximum displacement and a minimumdisplacement of the piezoelectric element by an average displacement.